The bit below from maximumpc magazine sums it up pretty well I think and describes the behavior or tendancy that I have personally experienced in the past. On every system I've built or worked on with the exception of perhaps servers we had the same attitude I think as this article, just one more unneeded inconvenience in getting a system built and or fixed and out the door. I see the potential benefit but I think in most home user installations it's not needed. The article notes that the default is off which is I believe how I have always encountered it. This is just one of those things that unless you have a need for it you just plain aren't going to use it on a daily basis. The only reason I would expect to encounter this in the field is either in a server installation or in a custom built setup with hot swappable drives in a very high end workstation. I would be very surprised to find this enabled in say a brand new Dell unless it was an expensive high end system for example. For the last two years or so I've done about 95% laptops so this doesn't come up ever, let alone RAID.
From
http://www.maximumpc.com/article/features/old_tech_new_tweaks?page=0%2C3
Odds and Ends
Before you POST your new system to install the OS, you should disable unneeded ports and make your decision to run either AHCI or IDE
When we build a new system, one of the first things we do is flip through the BIOS, turning off things we know we won’t ever use, such as the serial port and parallel port. If your system doesn’t include a floppy drive (some still do), we also flip off the floppy controller in the BIOS. Turning these features off saves some system resources, but it mostly just makes us feel good.
Turning on AHCI mode will require installing drivers via F6 with Windows XP.
Turning on AHCI mode will require installing drivers via F6 with Windows XP.
If you dig into your BIOS you’ll also see a setting that lets you configure your SATA ports as IDE, RAID, or AHCI. Default should be IDE and most people understand that setting RAID turns on the RAID features of the chipset, but just what is AHCI? It’s the Intel specification dubbed Advanced Host Controller Interface that enables such fancy features as native command queuing and hot-plugging of SATA devices. If you leave AHCI off, your drives will run in an emulated IDE mode.
The rub is that AHCI is not supported in Windows XP natively. You will have to use a floppy drive and F6 drivers or create a slipstreamed version of XP with AHCI drivers just to install the OS. If you already have Windows XP installed, flipping on AHCI will prevent the OS from loading. It’s also not clear what level of AHCI support Vista has, but if you install with AHCI on, you don’t need to install drivers. If you install Vista in IDE mode, however, and then turn on AHCI mode in the BIOS, the OS bluescreens.
Do NCQ and hot-plugging make AHCI worthwhile? For the most part, no. NCQ can actually hurt performance in some situations. Still, there have been online reports of chipsets performing quite poorly unless AHCI is enabled. AHCI is supported only by Intel and ATI at this point and not by Nvidia.
